The invention relates to a device and a method for starting an internal-combustion engine arranged in a vehicle. The following are provided for starting the internal-combustion engine: an electric machine designed for at least temporarily driving the internal-combustion engine, and a storage unit designed for at least temporarily supplying the electric machine with electric energy. Furthermore, the vehicle has a number of consumer assemblies which can be driven at least temporarily by the internal-combustion engine by way of a respective process-specific connection.
Vehicles are currently used which require a starting behavior that is modified in comparison to that of a conventional vehicle. This applies, for example, to a vehicle that is equipped with a so-called automatic start-stop system, or also to a hybrid vehicle. By means of an automatic start-stop system, the internal-combustion engine is switched off when the vehicle is at a standstill or when there is a falling below a vehicle speed threshold value. In the case of a hybrid vehicle, particularly in the case of a vehicle constructed as a parallel hybrid, an internal-combustion engine as well as an electric machine are provided for the propulsion. A hybrid vehicle can therefore be moved along even though the internal-combustion engine is switched off or cut off because the electric machine is available for that purpose. The modified starting behavior is connected with new operating strategies, which are conceivable by means of these vehicles or become necessary for these vehicles.
In the case of a conventional vehicle, a first start or initial start of the internal-combustion engine is carried out, which is triggered for the first time by the driver after entering the vehicle at the start of the drive. During a first start, it is not necessary for the internal-combustion engine to provide a defined large torque within a very short time, particularly a torque that correlates with a present vehicle movement condition.
In the case of a vehicle having an automatic start-stop system, in addition to the first start, also a restart and, if the vehicle is constructed as a hybrid vehicle, if required, also an additional start of the motor vehicle has to be carried out. In the case of a restart as well as in the case of an additional start, there is at first no process-specific connection of the internal-combustion engine with the driven wheels of the vehicle, but it is imminent. The restart and the additional start are caused by a control unit installed in the vehicle.
A restart that is to be carried out is recognized when a start-driving signal is present in a defined first vehicle operating state, in which case, this first vehicle operating state may be an idle state of the vehicle in which the vehicle is stationary (vehicle speed=zero), or it may be a first vehicle movement state in which the vehicle has a vehicle speed that is lower than a first threshold value or greater than a second threshold value and lower than a third threshold value. In this vehicle operating state, the internal-combustion engine may be stopped or have a rotational engine speed which is between a cut-off rotational speed and the zero value. An additional start to be carried out is recognized when, in a defined second vehicle operating state, an engine torque demand is present, in which case this second vehicle operating state is a second vehicle movement state, in which the vehicle has a vehicle speed which may assume an arbitrary value from a large range of values, this value range extending from a vehicle speed close to the zero value to a very high vehicle speed, which is defined by the electric driving mode of the hybrid vehicle. Also in this vehicle operating state, the internal-combustion engine may be stopped or have an engine rotational speed which is between a cut-off rotational speed and the zero value. In the idle state of the vehicle as well as in the movement states of the vehicle, the focus is on the fact that the internal-combustion engine is either stopped (rotational engine speed=zero) or carries out a diminishing or decreasing rotational engine movement, the rotational engine speed therefore being between a cut-off rotational speed and the zero value.
The start-driving signal represents an immediately imminent driving start of the vehicle, which is to begin from the idle vehicle state or the first vehicle movement state. It should preferably be a driving start initiated by the driver. The start-driving signal is, for example, a signal which represents the actuation of the clutch pedal by the driver. As an alternative, it may also be an automated driving start that is therefore initiated independently of the driver. The engine torque demand represents a torque which is to be set by the internal-combustion engine in the respective second vehicle movement state in a manner that is dependent on or independent of the driver. A torque to be set in a manner that is dependent on the driver occurs, for example, as a result of an actuation of the accelerator pedal by the driver. In this case, the engine torque demand may therefore be a quantity representing the accelerator pedal actuation. A driver-independent engine torque demand may be generated, for example, by a longitudinal control system, in which case, the longitudinal control system may preferably be an adaptive cruise control system. The cut-off rotational speed is that rotational engine speed of the internal-combustion engine that is present during the cutting-off of the internal-combustion engine, i.e. during or immediately after the interruption of the operative connection to the driven wheels, for example, caused by the actuation of the clutch. The cut-off rotational speed may correspond to the idling rotational speed. However, depending on the operation, it may temporarily be above the idling rotational speed or already below the idling rotational speed.
The restart as well as the additional start of the internal-combustion engine differ from the initial start. During a restart, for example, at a traffic light, a high torque is to be provided within a very short time by the internal-combustion engine; the internal-combustion engine is started more rapidly than during an initial start. During the additional start of the internal-combustion engine, the internal-combustion engine has to provide within a very short time a torque correlating with the vehicle movement state; a very rapid pulling-up of the internal-combustion engine to a desired rotational engine speed is required (reflex start). Compared to an initial start, a restart as well as an additional start are so-called reflex starts.
In the case of a hybrid vehicle, in addition to the initial start, an additional start of the internal-combustion engine also has to be carried out. If the hybrid vehicle is equipped with an automatic start-stop system, a restart of the internal-combustion engine also has to be carried out. In this case, the above-mentioned statements made concerning a vehicle with an automatic start-stop system apply correspondingly.
As mentioned above, it may be necessary to carry out a restart or an additional start of the internal-combustion engine in a vehicle operating state in which a diminishing or decreasing rotational movement of the engine is present, and the internal-combustion engine is therefore in an internal-combustion engine operating state with a rotational engine speed decreasing to a stop. Such a situation may occur, for example, when, at a first point-in-time, an internal-combustion engine stop condition or cut-off condition has been met and, at a later, second point-in-time, an internal-combustion engine start condition has been met, in which case the second point-in-time is within that time period within which the rotational engine speed of the internal-combustion engine decreases or goes to zero. In the least favorable case, the second point-in-time immediately follows the first point-in-time; i.e. the rotational engine speed of the internal-combustion engine existing at the second point-in-time has not yet significantly decreased in comparison to the first point-in-time. In such a “change-of-mind situation”, in contrast to the original intention to stop or cut-off the internal-combustion engine, a continued operation or restarting or additional starting of the internal-combustion engine is now desired. An internal-combustion engine stop condition or cut-off condition exists, for example, when the vehicle is in the vehicle idle state or in one of the two vehicle movement states and the operative connection between the internal-combustion engine and the driven wheels of the vehicle is interrupted. Concerning the internal-combustion engine start condition, reference is made to the statements made above.
A “change-of-mind-situation” may occur, for example, when a vehicle having an automatic start-stop system comes to a stop at a red traffic light and, because of the presence of the internal-combustion engine stop condition, the internal-combustion engine is cut off, but, immediately after the initiation of the cut-off operation, because of a signal change of the traffic light, a continued drive becomes possible which is why a start-driving signal is generated and the combustion engine has to be started again. At the point-in-time of the restart, the internal-combustion engine has a decreasing rotational-speed course. Such a situation may also occur in the case of a hybrid vehicle when, in a driving situation, the internal-combustion engine is cut off and the propulsion of the vehicle takes place exclusively by the electric machine but, immediately after the initiation of the cut-off operation, because of an unpredictable change in the driving operation or in the driving situation, an engine torque demand for the internal-combustion engine is present and the internal-combustion engine has to be started additionally. At the point-in-time of the additional start, the internal-combustion engine has a decreasing rotational-speed course. In the case of such driving-maneuver-relevant restart or additional-start demands, the starting operation of the internal-combustion engine has to take place as rapidly as possible from different cut-off rotational speeds of the internal-combustion engine. A so-called reflex start has to be carried out.
The following problem will now occur in the case of a reflex start, during which a restart or additional-start operation of the internal-combustion engine therefore is to take place immediately after the initiation of the cut-off operation: As a result of the fact that the restart or additional-start operation takes place immediately following the cut-off operation, the rotational speed of the internal-combustion engine has not yet significantly decreased with respect to the cut-off rotational speed. However, it is a fact that conventional engine-bound 12V starters can take over and restart the internal-combustion engine only at a sufficiently low rotational engine speed of the internal-combustion engine, in which case the sufficiently low rotational engine speed is clearly below the cut-off rotational speed and preferably close to the rotational speed of zero. This would mean that when such a conventional starter is used, a correspondingly long time period would have to pass and there would have to be a waiting period before a restarting or additional starting operation could be initiated. This time gap leads to an impairment of the vehicle drivability and is therefore perceived as a disadvantage by the driver, which makes it unacceptable.
Starting systems are nevertheless already commercially available which are reflex-start-capable and by means of which, immediately after the initiation of a cut-off operation, a restart or additional-start operation can therefore be carried out. In the case of such starting systems, specially designed electric machines are used for driving the internal-combustion engine, such as so-called freewheel-bound pinion starters. However, such pinion starters have the disadvantage that they are expensive and cannot be used in all vehicle types.
It is therefore an object of the present invention to further develop a device and a method of the above-mentioned type in order to be able to implement as rapidly as possible, following an already initiated cut-off operation, a restart or additional start of an internal-combustion engine and to thereby reduce or eliminate the impairment of the vehicle drivability caused by the deceleration time of the internal-combustion engine. In particular, it should be possible to be able to implement a reflex start by use of a conventional starter, i.e. to be able to carry out, immediately following an initiated cut-off operation, a restart or additional start of the internal-combustion engine. On the whole, a cost-effective device that is easy to implement and a corresponding method are to be provided wherein the additional-start or restart availability is increased in so-called “change-of-mind-situations”.
This and other objects are achieved by a device of the above-mentioned type which has a control unit designed for controlling at least one consumer assembly when a consumer assembly control condition is present, in order to generate and/or to increase a load affecting the internal-combustion engine, and subsequently to control the electric machine for driving the internal-combustion engine, when an internal-combustion engine start condition is present.
The object is further achieved by a method of the above-mentioned type, wherein the following steps take place in a control unit:
(a) controlling at least one consumer assembly when a consumer assembly control condition is present, in order to generate and/or to increase a load affecting the internal-combustion engine, and
(b) controlling the electric machine for driving the internal-combustion engine, when an internal-combustion engine start condition is present.
The device according to the invention and the method according to the invention are based on the following. Via an intelligent operating strategy by which consumer assemblies, which are installed in the vehicle anyhow and are therefore connected when a consumer assembly control condition is present, a load acting upon the internal-combustion engine is generated or a possibly already present load is increased. This change in the load acting upon the internal-combustion engine (either starting from the zero load value or a load value different from zero), in the case of a decelerating internal-combustion engine, results in a change in the braking torque and thus in the engine rotational speed, more precisely, in an increased reduction of the rotational engine speed. As a result, the deceleration time of the internal-combustion engine, which is the time period which passes until the internal-combustion engine, starting from a cut-off rotational speed, reaches an engine rotational speed at which the electric machine can take over the internal-combustion engine for implementing a restart or an additional start, is considerably reduced. It thereby becomes possible to be able to carry out a restart or additional start of the internal-combustion engine immediately after an initiated cut-off operation, even if the vehicle is equipped with a conventional starter. A reflex start can therefore be carried out by use of a conventional starter. The impairment of the vehicle drivability caused by a disproportionately long deceleration time of the internal-combustion engine can therefore be reduced or eliminated, whereby the availability of an additional start or a restart is increased in so-called “change-of-mind situations”. In addition, the invention can easily be integrated in current starting and vehicle power supply configurations, since only a software adaptation is required for this purpose.
The above-mentioned object has therefore been completely achieved.
In a further development of the invention, the consumer assembly control condition will exist when an operative connection between the internal-combustion engine and the driven wheels is interrupted and the internal-combustion engine has, at least temporarily, a decreasing internal-combustion engine rotational-speed course. By means of this condition, it can be unambiguously and reliably determined whether a vehicle operating condition is present in which the consumer assemblies installed in the vehicle are to be controlled and therefore to be connected, in order to achieve a reducing of the deceleration time of the internal-combustion engine. The unambiguousness and reliability is achieved in that, in addition to the internal-combustion engine stop condition—the operating connection between the internal-combustion engine and the driven wheels is interrupted—, it is checked whether the rotational engine speed of the internal-combustion engine is decreasing. Theoretically and therefore as an alternative, it would also be sufficient for only the internal-combustion engine stop condition to be examined as a consumer assembly control condition.
In a further development of the invention, the internal-combustion engine start condition is present when, in a first vehicle operating state, a start-driving signal is present and/or when, in a second vehicle operating state, an engine torque demand is present. It can therefore be unambiguously determined whether or when a restart (first vehicle operating state) or an additional start (second vehicle operating state) of the internal-combustion engine is required. Preferably, the first vehicle operating state is a vehicle idling state, in which the vehicle is stationary, or a first vehicle movement state, in which the vehicle has a vehicle speed that is lower than a first threshold value or which is greater than a second threshold value and lower than a third threshold value. The invention can therefore be used in the case of a restart to be carried out in a vehicle idling condition as well as in the case of a restart to be carried out in a vehicle movement condition. The first threshold value may, for example, be close to zero, preferably have the value of 3 km/h, which occurs in the case of vehicles equipped with a conventional automatic start-stop system.
In the case of such a conventional automatic start-stop system, the first threshold value may preferably also amount to 5 km/h or even 7 km/h. In the case of vehicles which are equipped with a further developed automatic start-stop system, the first threshold value may be in a range of from 20 km/h to 50 km/h. Preferably, the first threshold value amounts to 20 km/h, 30 km/h or 50 km/h. The second threshold value may have the values 3 km/h, 5 km/h or 7 km/h, and the third threshold value may have the values 20 km/h, 30 km/h or 50 km/h. The vehicle idling state is defined such that the vehicle is stationary (vehicle speed=zero). Further, the second vehicle operating state preferably is a second vehicle movement state, in which the vehicle has a vehicle speed which can assume an arbitrary value from a large value range. This value range extends from a vehicle speed close to the zero value to a very high vehicle speed which is defined by the electric driving mode of the hybrid vehicle. The additional start of the internal-combustion engine should therefore be possible starting from very low vehicle velocities almost close to zero, to very high vehicle velocities which may, for example, be at 50 km/h or 70 km/h or 100 km/h or at clearly higher values.
The invention can advantageously be used in differently configured vehicles, thus, for example, in a vehicle having an automatic start-stop system, in which case it is insignificant whether the vehicle is equipped with a manual transmission or an automatic transmission. The automatic start-stop system may be constructed such that the internal-combustion engine stop condition is present when the vehicle is stationary (vehicle speed=zero) or when the vehicle has a vehicle speed that is lower than a first threshold value or when the vehicle has a vehicle speed that is greater than a second threshold value and lower than a third threshold value. The invention may also be used in a hybrid vehicle. The invention can preferably also be used in a vehicle which has a restarting functionality as well as an additional starting functionality, thus, for example, in the case of a hybrid vehicle with an automatic start-stop system.
Furthermore, the invention can advantageously be used within the scope of the implementation of an arbitrary starting operation, which is to be carried out during the driving operation of a vehicle and which differs from a first or initial start.
In a further development of the invention, the control unit is further designed for controlling the electric machine for driving the internal-combustion engine when a value representing the internal-combustion engine rotational speed is lower than or equal to a threshold value. By means of this measure, it is ensured that the electric machine will not be controlled before the rotational engine speed of the internal-combustion engine has reached a value at which, without any problems and without being damaged in the process, the electric machine can take over the internal-combustion engine and can therefore start it again. This permits the use of conventional starters. In this case, it may be provided that the threshold value corresponds to a value different from zero, which means that the electric machine takes over or restarts a decelerating internal-combustion engine. However, it may also be provided that the threshold value corresponds to the zero value, which means that the electric machine takes over or restarts a stopped internal-combustion engine.
In a further development of the invention, the control unit is, in addition, designed for terminating the controlling of the consumer assembly when the internal-combustion engine start condition is present. As a result of this measure, it is ensured that, as soon as the starting operation begins, by which the internal-combustion engine is started, particularly is to be restarted or additionally started, the generated or increased load acting upon the internal-combustion engine is no longer present, and thereby the internal-combustion engine can be started as rapidly as possible and can generate a defined desired torque. As an alternative or in addition, the controlling of the consumer assembly can also be terminated when the value representing the internal-combustion engine rotational speed is lower than or equal to the pertaining threshold value.
In a further development of the invention, the control unit is further designed for making the number of the consumer assemblies to be controlled dependent on the internal-combustion engine rotational-speed value which is present at the point-in-time at which the consumer assembly control condition has been met, in particular, has been met for the first time. As an alternative or in addition, the control unit is further designed for making the type of control of the consumer assembly dependent on the internal-combustion engine rotational speed value which is present at the point-in-time at which the consumer assembly control condition has been met, particularly has been met for the first time. This measure permits a flexible controlling of the consumer assemblies that is adapted to external circumstances. Thus, it is contemplated to control, during a cut-off operation, which is initiated starting from a high cut-off rotational speed, a larger number of consumer assemblies than during a cut-off operation which is initiated starting from a lower cut-off rotational speed.
As a supplement or alternative, it is also contemplated to control, during a cut-off operation, which is initiated starting from a high cut-off rotational speed, a consumer assembly in such a manner that, as a result, a greater load acts upon the internal-combustion engine than during a cut-off operation that is initiated starting from a lower cut-off rotational speed. It is thereby ensured that the internal-combustion engine can always be restarted or additionally started as rapidly as possible, independently of the amount of the cut-off rotational speed from which the cut-off operation is initiated.
In a further development of the invention, one of the consumer assemblies is a generator which is designed for charging the storage unit at least temporarily. In this case, the control unit is designed for controlling the generator in the presence of the consumer assembly control condition in such a manner that the generator supplies a maximally possible charging current. This measure has the following advantage: the controlling of the consumer assemblies according to the invention for generating or increasing a load acting upon the internal-combustion engine has the result that electric energy is consumed. When now the generator is controlled for the purpose of increasing the load or generating the load, not only energy will be consumed but, to a certain extent, energy is also generated again, which can be stored in the storage unit. This contributes to a favorable energy balance and therefore to a lower fuel consumption.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.